(1) Field of the Invention
The present invention relates to an aluminum-beryllium-silicon based alloy to be favorably used for producing automobile engine parts, etc.
(2) Related Art Statement
Automobile engines, particularly high-performance engines, are required to operate at high rpms to generate high outputs, and therefore lighter high-strength materials, that is, materials having higher specific strengths, are demanded for this requirement.
Further, weight reduction is also important for enhancing drivability. In order to prevent drop in rigidity even if thinned or lighter materials are used, lighter materials having higher Young""s modulus, that is, materials having higher specific moduli of rigidity are required.
Furthermore, from the standpoint that outputs are ensured by keeping a clearance constant against changes in temperature, materials having smaller coefficients of thermal expansion and excellent wear resistance and heat resistance are demanded.
In addition, as viewed from the manufacturing methods, moving parts of the high-performance engines are made mainly of forged products which can fully exhibit the potentials of the alloys thereof, so that materials having excellent plastic workability are desired. Casings and the like having thin and complicated shapes can be produced by casting only. Therefore, castable alloys are naturally desired.
Under the above circumstances, Alxe2x80x94Si based aluminum alloys have been generally used for engine parts. In order to increase the specific strength of such alloys, primary Si crystals are made finer by quenching or a highly heat-resistive hard ingredient is incorporated.
For example, materials having strength and toughness enhanced by quenching in powder metallurgy are reported in xe2x80x9cLight metals, Vol. 49, No. 4, 1999, pp 178-182, and composite materials (MMC) in which ceramic particles or intermetallic compound particles are dispersed in an Al matrix are reported in xe2x80x9cLight metals, Vol. 49, No. 9, 1999, pp 438-442.
However, since these materials have low ductility, it is difficult to shape them by conventional forging methods, and it is also difficult to use them for producing cast products.
Further, since their specific gravities are equivalent to or greater than that of Al, their specific strength does not rise, so that there remains a problem that it is difficult to realize high rpms to generate high outputs.
On the other hand, Al alloys in which an appropriate amount of Be is incorporated into Al have been known as materials having high specific moduli of rigidity for a long time. As examples of such alloys, Al alloys are proposed in U.S. Pat. Nos. 2,399,104, 5,578,146, etc.
However, since all of such alloys are produced by using the powdery metallurgy as a producing method, it is extremely difficult to plastically work the alloys into complicated shapes by forging.
On the other hand, for example, U.S. Pat. Nos. 5,417,778, 5,667,600, etc. disclose Al alloys which employ the casting method.
However, the Al alloys obtained by this method have tensile strengths of about 170 to about 320 MPa and low elongations of around 2%. However, if the alloy is extruded to cover these defects, primary crystals of Be are elongated to unfavorably increase anisotropy.
Al alloys into which Be is incorporated at high concentrations are likely to be expensive, so that such alloys can be used for limited purposes only.
The present invention has been developed in view of the above-mentioned circumstances, and is aimed at providing aluminum-beryllium-silicon based alloys which are not only light, of high specific modulus of rigidity and of high specific strength, but also have small coefficients of thermal expansion and excellent wear resistance and heat resistance with castability and plastic workability comparable to those of the conventional Al alloys.
The breakthrough history of the present invention will be explained below.
In order to realize the above objects, the present invention made investigations on elements effective to enhance wear resistance and reduce the coefficient of thermal expansion with respect to Al as a base material. As a result, they discovered that Si is useful as such elements, and discovered that if Si is incorporated in an amount of not less than 0.1 mass % (preferably and less than 5 mass %), excellent wear resistance and advantageously reduced coefficient of thermal expansion can be attained.
Next, the present invention made investigations upon elements to reduce the specific gravity and increase the specific modulus of rigidity with respect to the above Alxe2x80x94Si alloys, and came to know that Be is effective.
However, it was also discovered that the addition of Be increases the specific modulus of rigidity but unfavorably decrease strength at high temperatures.
In view of this, the inventors then repeatedly made strenuous investigations to prevent reduction in the strength of high temperatures due to the decreased specific gravity. As a result, the present inventors came to know that the addition of Mg is extremely effective for realizing this purpose.
It was also discovered that Cu, Ni, Co, Fe and a very small amount of Y or Ti are effective as ingredients for enhancing strength at high temperatures.
Particularly, it was further discovered that the addition of Fe makes crystals of Be granular, which facilitates working such as extrusion.
The present invention was accomplished based on the above knowledge.
(1) The present invention relates to an aluminum-beryllium-silicon based alloy comprising 5.0 to 30.0 mass % of Be, 0.1 to 15.0 mass % of Si and 0.1 to 3.0 mass % of Mg, the balance being Al and inevitable impurities.
As the aluminum-beryllium-silicon alloy (1), the following are preferable.
(2) The aluminum-beryllium-silicon based alloy further comprises at least one of 0.1 to 3.0 mass % of Cu, 0.05 to 1.5 mass % of Ni, 0.05 to 1.5 mass % of Co and 0.05 to 1.5 mass % of Fe.
The aluminum-beryllium-silicon based alloy (1) or (2) further comprises 0.01 to 0.8 mass % of Y and 0.01 to 0.1 mass % of Ti.